Systems and method for optimization of laser beam spatial intensity profile

ABSTRACT

A thin beam directional crystallization system configured to process a substrate comprises a laser configured to produce laser light, the laser configured to have a high energy mode and a low energy mode. The high energy mode is configured to produce light energy sufficient to completely melt a substrate coated with amorphous silicon film, while the low energy mode is configured to produce light energy that is not sufficient to completely melt a substrate coated with amorphous silicon film. The system further comprises beam shaping optics coupled to the laser and configured to convert the laser light emitted from the laser into a long thin beam with a short axis and a long axis, a stage configured to support the substrate and film, and a translator coupled with the stage, the translator configured to advance the substrate and film so as to produce a step size in conjunction with the firing of the laser.

RELATED APPLICATIONS INFORMATION

This application claims priority as a continuation in part under 35U.S.C. 120 to U.S. patent application Ser. No. 11/381,052, entitled“Systems and Methods for Optimization of Laser Beam Spatial Intensity,”filed May 1, 2006, which is incorporated herein in its entirety as ifset forth in full.

BACKGROUND

1. Field of the Invention

The field of the invention relates generally to, Liquid Crystal Displays(LCDs), and more particularly to systems and methods for manufacturingLCDs.

2. Background of the Invention

There is already a well-established and growing market for active matrixLCDs, in which an active thin film transistor (TFT) is used to controleach pixel in the display. For example, active matrix LCDs are theprevailing technology for computer screens. Additionally, in recentyears, active matrix LCD solutions also have made dramatic inroads inmarket segments such as televisions, mobile phones, PDAs, videorecorders, etc.

Active matrix LCDs are predicted to be the fastest growing segment ofthe display industry, with a projected average annual growth rate of 35percent over the next five years. In contrast, passive LCDs andconventional cathode ray tubes (CRTs), are predicted to have flat tonegative growth rates. The only other display technology predicted tohave positive growth is Organic Light Emitting Diode (OLED) displays,which is just now emerging for specialized applications and is predictedto more than double each year beyond 2007.

In addition to rapid overall growth, the nature of the LCD market ischanging, i.e., newer LCD applications include a more diversity and morespecial requirements. For example, phones represent approximately 50percent of all LCDs but only 2 percent of total LCD area. In contrast,monitors represent approximately 27 percent of LCDs but 50 percent ofthe total area. With rapid growth of TV applications and large screensizes, televisions are projected to comprise more than 30 percent of thetotal LCD area by 2008. These large screen applications have manyspecial requirements compared to previous LCD applications.

To support the expected high growth rates and to successfully competefor new market opportunities, LCD manufacturers must be able to leverageemerging display fabrication techniques to improve the features andperformance of the LCD offerings, while simultaneously improving theirproduction costs and throughput.

As the LCD industry moves into the next phase of rapid growth andproduct diversity, some factors for success can include smaller pixelsize, higher densities, which are a direct function of the size of theTFTs, and higher TFT switching speeds to support video requirements.Brighter display capabilities, improved aperture ratios for more lightper pixel, and overall lower production costs are also factors forsuccess. Lower production costs can result from both faster processingthroughput and a consistently higher yield of good displays per panel.For long term success, it will be important for LCD manufacturers toinvest in technology solutions that can also be cost-effectively adaptedfor efficient fabrication of emerging high-growth screen types such asOLED.

The two primary process methods that are currently used for creating aconductive layer on a glass substrate that will support the fabricationof TFTs for active matrix LCDs are Amorphous silicon (a-Si) and Lowtemperature polycrystalline silicon (poly-Si or LTPS). In the a-Siprocess, a gate layer is created directly on PECVD Si film. In thepoly-Si or LTPS process, the PECVD Si film is crystallized prior to gatefabrication to produce higher performance TFTs. In these processes thetemperature is kept low to avoid melting the glass substrate. Becausethe movement of electrons is inherently slower through amorphous silicontransistors, a-Si based TFTs have to be physically larger in order toprovide sufficient current flow from source to drain. On the other hand,due to the significantly higher electron mobility that can be achievedwith poly-silicon, LTPS based TFTs can be smaller and faster. Becausepoly-silicon transistors are inherently smaller, more light can passthrough each pixel. This allows design flexibility to allow for improvedaperture ratios, greater pixel densities, or both.

Despite the TFT size and performance advantages of LTPS, most LCD panelstoday are still fabricated using an amorphous-silicon process. This isdue primarily to the relatively lower costs of a-Si that result fromfewer process steps and the potential unknowns associated with lessmature LTPS equipment. A-Si also has been a “safe” process forminimizing costs, since a single defect in a large screen LCD meansscrapping the whole device; however, even though a-Si processes arefairly well established and controllable, it has now become clear thata-Si technology is approaching its limitations with regard to supportingthe emerging demand for higher pixel densities, faster response, andbrighter displays.

To date, LTPS has typically been targeted at fabricating smaller, higherperformance displays because the smaller physical size of poly-siliconbased TFTs allow for increased screen brightness, higher pixel density,and lower energy consumption. Also, the inherently faster switching ofLTPS transistors supports the requirements of video applications such asvideo recorders as well as video features in cell phones and PDAs.

Display manufacturers also need to plan ahead for the emergence ofOrganic Light Emitting Diode technology, which will become a significantsegment of the display market with rapid growth projected to begin in2007. Some simple OLED devices are already being deployed forspecialized applications, such as small-screen, high brightness displaysfor automotive instruments and digital cameras. Several companies haveannounced their intention to produce large-screen OLED displays that,when productized, will gain significant market share for applicationswhere display brightness and color is a key differentiating factor.

In OLED-based displays, the molecular structure actually emits lightrather than acting as a light valve for a backlit light source, thusenabling much brighter screens. Because the light-emitting material inOLED is current-driven, rather than voltage-driven as in LCDs, thehigher electron mobility and more stable current capacity ofpoly-silicon will be a key enabler for OLED implementation. The inherenthigher luminescence of OLED also will allow designers to opt for smallerpixels to produce the same brightness, thereby enabling higherresolutions. Implementation of OLED displays will therefore be much morecompatible with the smaller geometries achievable through poly-silicon.

Moving forward, display manufacturers need to deploy panel fabricationtechnologies that can provide high-throughput, high-yield capacity forpoly-silicon production to meet today's diverse, rapidly growing LCDrequirements while also laying the foundation for future, e.g., OLEDmarket ramp-up. LCD or OLED fabrication methodology can focus on threeareas: producing high-performance TFTs, yielding uniform material anddevices across the entire panel, and optimizing production efficiencythrough a combination of high throughput and low operational costs.

The most widely used LTPS fabrication techniques involve a surfacetreatment that uses a laser to melt a silicon film, heating it to aliquid point over a very short time period, generally measured innanoseconds, after which the Si film recrystallizes into polycrystallinesilicon. The primary challenges in LTPS technologies involve theeffective control of the process to assure uniform crystallizationacross the entire panel while providing a high level of sustainedprocess throughput and low operational costs.

SUMMARY

A thin beam crystallization system configured to process a substratecomprises a laser configured to produce laser light, the laserconfigured to have a high energy mode and a low energy mode. The highenergy mode is configured to produce light energy sufficient tocompletely melt a silicon substrate, while the low energy mode isconfigured to produce light energy that is not sufficient to completelymelt a silicon substrate. The system further comprises beam shapingoptics coupled to the laser and configured to convert the laser lightemitted from the laser into a long thin beam with a short axis and along axis, a stage configured to support the silicon substrate, and atranslator coupled with the stage, the translator configured to advancethe silicon substrate so as to produce a step size in conjunction withthe firing of the laser.

In one aspect, the system can be configured to perform one type ofannealing process, such as ELA, in the low energy mode, while performinganother type of annealing process, such as Thin-beam DirectionalCrystallization, when in the high energy mode. In this manner, theprocess selecting can be optimized for particular areas to be formed onthe substrate.

These and other features, aspects, and embodiments of the invention aredescribed below in the section entitled “Detailed Description.”

BRIEF DESCRIPTION OF THE FIGURES

Features, aspects, and embodiments of the inventions are described inconjunction with the attached drawings, in which:

FIG. 1 is a diagram illustrating an example cross section of a filmsurface after a single pulse irradiation;

FIG. 2 is a diagram illustrating another example cross section of a filmsurface after a single pulse irradiation;

FIG. 3 is a diagram illustrating an example position of a beam during asecond irradiation of the cross section of a film surface of FIG. 1;

FIG. 4 is a diagram illustrating an example scattering of incidentphotons during the second irradiation illustrated in FIG. 3;

FIGS. 5A-5C are diagrams illustrating example short-axis spatialintensity profiles;

FIG. 6 is a diagram illustrating an example position of a beam after “n”pulses;

FIG. 7 is a diagram illustrating a beam spatial intensity and an exampleposition of a beam after “n+1” pulses;

FIG. 8 is an example device for manufacturing a liquid crystal display;and

FIG. 9 is a diagram illustrating an amorphous silicon coated glasspanel.

DETAILED DESCRIPTION

Thin-beam Directional Crystallization, or Thin-beam Directional'Xtallization (TDX), fabrication methods can combine poly-silicon'sinherent advantages with efficient volume-oriented productioncapabilities. The end result can be superior electron mobility, flatsurface topology, a large process window, and greater throughput.Different types of lasers can be used in thin-beam directionalcrystallization, for example, in one embodiment a solid state laser canbe used. In another embodiment a high energy Excimer laser can be usedin the TDX process. A master oscillator power amplifier (MOPA)configuration that was originally developed for semiconductor ofmicrolithography applications can also be used. The laser can operate at351 nanometers and provide over 900 watts of power with exceptionalpulse-to-pulse stability and high reliability. Other wavelengths canalso be used, for example, 308 nanometers. Generally, any wavelengththat is strongly absorbed by the material to be melted, e.g., silicon,can be used. A TDX system is described in co-pending U.S. patentapplication Ser. No. 10/781,251 entitled “Very High Energy, HighStability Gas Discharge Laser Surface Treatment System,” filed Feb. 18,2004; U.S. patent application Ser. No. 10/884,101 entitled “Laser ThinFilm Poly-Silicon Annealing Optical System,” filed Jul. 1, 2004; U.S.patent application Ser. No. 10/884,547 entitled “Laser Thin FilmPoly-Silicon Annealing System,” filed Jul. 1, 2004; and U.S. patentapplication Ser. No. 11/201,877 entitled “Laser Thin Film Poly-SiliconAnnealing Optical System,” filed Aug. 11, 2005, which are incorporatedherein by reference as if set forth in full.

The TDX optical system used in conjunction with the systems and methodsdescribed herein can convert laser light into a very long thin uniformbeam and deliver it onto the silicon substrate. In addition, it can beconfigured to stabilize the beam's energy, density and pointing; all ofwhich can improve the consistency of the TDX process. In one embodiment,each pulse can expose an area of approximately 5 microns wide and 730millimeters long. The length of the beam can be matched to the substratewidth so that the glass is processed in a single pass. This can help toensure a high degree of uniformity and rapid throughput. Duringexposure, the panel can be scanned at a constant velocity and the lasercan be triggered to fire at a pitch, or step size of, e.g., 2 microns.The pitch can be chosen so that the melt region always seeds from thehigh quality crystals of the previous pulse, producing long directionalpoly-silicon crystals. Each pulse also melts the large ridge orprotrusion at the center of the previous melt region, resulting in amore planer surface.

The TDX process is based on a form of controlled super lateral growthwhere the melt region re-solidifies laterally from the edges and towardsthe center. In contrast to ELA where crystal growth proceeds verticallyfrom within the silicon layer, lateral growth produces large directionalpoly-silicon grains with high electron mobility. The TDX process has amuch larger process window than ELA because it relies on spatiallycontrolled complete melting of the silicon film and avoids energysensitive partial film melting.

The use of a System on Glass (SOG) design approach is another evolvingarena that is only made possible with poly-silicon, and which will alsobenefit from the new TDX advances in LTPS process efficiency. The higherelectron mobility and smaller size transistors that are achievable withLTPS allow the drive electronics to be fabricated directly into the thinSi coating. This provides a powerful method to reducing panel cost andalso improves panel robustness by decreasing the need for tab bondconnections. Poly-silicon's much higher electron mobility allows foradditional integration of drive electronics such as integratingdigital-to-analog converter (DAC) on the substrate and reducing thenumber of drivers, e.g., by using faster drivers to control more TFTswitches.

The overall cost savings with SOG can be very dramatic, especially forprocessing large panels that consist of many small LCD screens. Using aconventional a-Si approach with separate tab bonded drive electronicsfor each screen, the drive chips can comprise a significant percentageof the cost per screen as well as an expensive additional assembly step.In comparison, SOG with poly-silicon allows the drive electronics to beefficiently fabricated during the backplane manufacturing process.

With this in mind, FIG. 1 is a diagram illustrating an example crosssection of a film surface 102 after a single pulse irradiation in athin-beam directional crystallization process in accordance with oneembodiment of the systems and methods described herein. Film surface 102can, for example, be amorphous silicon. The thin-beam irradiation meltsa portion of surface 102 using a laser. The melted portion generallyfreezes or solidifies from the sides inward to the middle of the meltedregion, leaving two laterally solidified regions 104 and 106. This isbecause each un-melted edge of silicon film 102 acts as a “seed” onwhich the melted silicon can grow.

Protrusions 108 can exist at the last point of freezing generally at ornear the center of the irradiated surface. Protrusion 108 can be causedwhen the two edges grow into each other. At or near the center where thetwo edges grow together the crystallized structures generally will notmatch because each edge is “seeded” from opposite sides of the meltedregion and these sides do not generally match each other. Where themismatched structures meet the crystals will push into each other andpush up from the surface. These protrusions 108 can be on the order of afilm thickness. The film thickness is commonly about 50-100 nm, however,other film thicknesses are possible.

Protrusion 108 breaks up the uniformed crystallized structure of thesurface. Further, as discussed above, the pattern of protrusions 108that appear after annealing can also make it difficult to deposit auniform gate dielectric layer, leading to non-uniformity in the TFTperformance across the panel. In order to remove protrusion 108 it canbe re-melted in the next laser shot.

For example, film surface 102 can be moved a certain step size under thelaser for the next shot. The step size must be set, however, to ensurethat sufficient laser energy is imported to protrusion 108 so as toensure protrusion 108 melts. Accordingly, the need to re-melt eachprotrusion 108, limits the maximum step size that can be achieved. Themaximum theoretical step size is equal to lateral growth distance 110,because the laser must re-melt protrusion 108. In the example of FIG. 1the lateral growth distance is equal to about one half the width of themelt region. Therefore, the theoretical maximum step size that can beused and still ensure that protrusion 108 is melted is equal toapproximately the lateral growth distance minus the width of protrusion108.

Generally, however, the step size must be kept much less than thetheoretical maximum, e.g., by several hundred nanometers where the laserpulse width is about 5 μm. This reduction reduces throughput. The actualstep size will be less than the maximum theoretical step size becausegreater energy is required to re-melt the protrusions 108. This isbecause protrusion 108 is thicker than the rest of film surface 102.Additionally, protrusions 108 can scatter the laser light. So, not onlywill it take more energy to re-melt protrusion 108 due to its thickness,more energy will also be needed to make up for laser energy scattered byprotrusion 108.

FIG. 4 is a diagram illustrating an example scattering of incidentphotons during irradiation. As incident photons 408 irradiate surface102 some of those photons 402 are scattered by protrusion 108. Thus,more energy can be required to melt protrusion 108. As discussed above,this scattering and the extra thickness of protrusion 108 can lower theachievable step distance and increase processing time of LCDs, becausemore energy is required to melt protrusion 108. Accordingly, a spatialintensity, short-axis profile that directs more energy at the locationof protrusion 108 can be used to maximize step size 304.

It should also be noted that the laser beam width must be controlled toavoid the formation of nucleated grains 204 as illustrated in FIG. 2.Nucleated grains can occur when the center cools before the sides cangrow together. When the center cools before the sides can grow together,its structure will generally not match the crystalline structure ofeither side, since it does not “seed” off of either side. Rather if thecenter cools faster than the sides can grow together it will seedvertically from within. This can occur if the melted region is too wide,i.e., the laser beam width is too wide. When the melted region is toowide the sides cannot grow together before the center solidifies.

If the beam is too wide, then as lateral solidified regions 206 and 208grow to the center nucleated region 204 and two protrusions 210 and 212can occur. Protrusions 210 and 212 can be caused when the edges growinto nucleated region 204. The crystallized structures of each lateralsolidified region 206 and 208 generally will not match nucleated region204 because each edge is “seeded” from opposite sides of the meltedregion. Where the mismatched structures meet the crystals will push intoeach other and push up from the surface. As discussed above, it isgenerally preferable that the crystallized structure of an LCD formedwhen the film surface 202 solidifies be uniform. Protrusions 210 and 212break up the uniform crystallized structure of the surface. Therefore,it can be advantageous to limit the beam width such that nucleatedregion 204 does not occur. For example, in one embodiment, the beamwidth is approximately 5 μm; however, it will be understood that thebeam width will depend on a particular embodiment. As long as each sidecan grow together before nucleation occurs, the fine-grain nucleatedregion 204 will not occur.

As discussed above, film surface 102 can be moved, or stepped underneaththe beam to melt protrusion 108. Surface 102 can, for example be movedto the left a little less than one half the pulse width. Protrusion 108can then be re-melted, along with a small portion of lateral solidifiedregion 104, all of lateral solidified region 106 and a portion ofun-irradiated amorphous-Si 114. As a lateral solidified region growsfrom the left to the right it will seed from lateral solidified region104, continuing the crystalline structure of lateral solidified region104 until meeting in the middle to form a new protrusion. This can beseen with respect to FIG. 3.

FIG. 3 is a diagram illustrating an example position of a beam during asecond irradiation of the cross section of a film surface of FIG. 1. Theposition of the beam during the first irradiation is shown at position302. As discussed above, film surface 102 can be moved underneath thebeam to melt the next section of surface 102. Surface 102 can, forexample, be moved to the left a step distance 304 which can be a littleless than one half the beam width. The beam will then be positioned at306 during the second shot, which will irradiate surface 102 withincident photons 308. Photons 308 can re-melt protrusion 108 along witha small portion 310 of lateral solidified region 104, all of lateralsolidified region 106 and a portion 312 of un-irradiated amorphous-Si114. As a new lateral solidified region grows from the left to the rightit will seed from lateral solidified region 104, continuing thecrystalline structure of lateral solidified region 104 until meeting inthe middle of the new melt region to form a new protrusion. The newprotrusion will form at approximately position 314.

FIG. 6 is a diagram illustrating an example position 602 of a beam after“n” pulses. Film surface 102 can be moved at a constant rate. Each pulsecan be timed to occur as film surface 102 moves one nominal step size604. As can be seen, successive lateral solidification regions 604, eachapproximately half the length of beam width 602, are produced as thelaser moves along the surface 102. As was discussed above, the nominalstep size 604 is generally less than the theoretical maximum step size,and the actual step size can be maximized by having an intensity peaknear protrusion 108.

Referring to FIG. 3, step distance 304 can be less than the theoreticalmaximum because it takes extra energy to re-melt protrusion 108 andlight can be scattered by protrusion 108. Processing can only proceed aseach section cools. Smaller steps can increase process time and wastetime re-melting area that was melted before. Small portion 310 oflateral solidified region 104 is re-melted by photons 308 from the beam.As will be understood, the larger the small portion 310, the longer itwill generally take to process film surface 102. Therefore, if smallportion 310 can be minimized, i.e., a larger step size can be achieved,then this can generally speed up the manufacture process leading tofaster processing time and larger production volumes.

FIGS. 5A-5C are diagrams illustrating example short-axis spatialintensity profiles that can be used to direct more energy at thelocation of protrusion 108. FIG. 5A shows a top-hat profile. Generally,a top hat profile with steep sides, such as that illustrated in FIG. 5A,is preferable because it results in a more uniform application of energyto the surface 102; however as noted, it can be preferable to directmore energy at protrusion 108 in order to increase the step size. Moreenergy can be directed at protrusion 108 by raising the energy densityof a beam with a top hat profile such as that illustrated in FIG. 5A.But generally it is not sufficient to simply raise the energy density ofthe beam with a top-hat spatial profile, as this could ultimately leadto film damage or agglomeration at the side of the beam which isincident upon the amorphous-Si film.

A laser beam short-axis profile that roughly correlates the intensityprofile of the beam to the required melting temperature of the film isgenerally preferred. The profile can be tailored to enable the maximumper-pulse step distance without exceeding the damage threshold. FIGS. 5Band 5C illustrate two short-axis profiles with intensity peaks occurringon the edge of the beam that correlates with the location of protrusion108. For example, proper control of the beam delivery and beam treatmentsystems as illustrated in FIGS. 8 and 9 of Co-pending U.S. patentapplication Ser. No. 10/884,547 entitled “Laser Thin Film Poly-SiliconAnnealing System,” filed Jul. 1, 2004, which is incorporated herein byreference as if set forth in full, can be used to manipulate theshort-axis spatial intensity profile.

FIG. 7 is a diagram illustrating the use of a beam 712 with ashort-axis, spatial intensity profile similar to that illustrated inFIG. 5 b. As was discussed above, a short-axis laser beam profile thatroughly correlates the intensity profile of the beam to the requiredmelting temperature of the film is generally preferred. As can be seenin FIG. 7 the intensity is highest near protrusion 108. In this way moreenergy can be supplied to provide the additional energy that can berequired to melt protrusion 108 due to increased thickness andscattering, as discussed above. Because more energy is contained in theleft hand side of the short-axis profile, the step size 704 can beincreased, such that it more closely approaches the theoretical maximum,but still ensures adequate melting of protrusion 108.

In other words, by using a short axis, spatial intensity profile, suchas illustrated in FIGS. 5B and 5C, portion 310 can be reduced and thestep size can be increased. It will be understood that the increase insize will depend on the implementation, but that the step size can benearer to the theoretical maximum due to the increased intensity of thebeam at the location of protrusion 108. The step size can, for example,be increased up to several hundred nanometers for a sum beam width.

FIG. 8 is an example surface treatment system 800 for manufacturing aliquid crystal display in accordance with one embodiment of the systemsand methods described herein. Thin-beam Directional Crystallization asdescribed above, combines the benefits of lateral crystal growth withhigher throughput, improved poly-Silicon uniformity and tailoring theshort-axis spatial intensity profile to the energy required to the meltsilicon film.

Using a specially designed laser 802 and custom beam forming optics 804,substrate 809 can be exposed with a long thin beam 808. A beam formingoptical system 804 can produce a short-axis spatial laser beam profile,e.g., as discussed above with respect to FIGS. 5A and 5B. In oneembodiment long thin beam 808 can measure 5 microns wide by up to 730 mmlong. This beam configuration can allow for complete coverage across thewidth of a glass substrate 809 during a single laser pulse. Because a 5microns wide region is rendered completely molten, the Siliconsolidifies by lateral growth crystallization, resulting in high mobilitypoly-Si. To process the entire substrate 809, the glass can be scannedbeneath the beam 808 so that the crystallization occurs in a singlepass. The glass can move at a constant velocity, and the laser can betriggered to fire after a translation of approximately 2 μm. Byoverlapping each new “stripe” over the previous one, a new stripe can be“seeded” from good poly-Si of the previous stripe, and the system canachieve continuous growth of a long, uniform crystal grains across theentire substrate 809.

The practical realization of the Thin-beam Directional Crystallizationcan include, for example, three major components in the system: thelaser 802, the beam forming optics 804 and the stage 810. In oneembodiment a specially designed high power laser 802 with a carefullychosen combination of power, pulse frequency and pulse energy to supportthe long beam and high scan rates can be used. This laser 802 can, forexample, provide 900 W of power, which is almost three times thecurrently available laser power, to ensure the highest throughput. Inone embodiment a laser 802 originally designed for the demandingsemiconductor lithography application can be used to ensure gooduniformity of the poly-Si and the TFT performance throughout thesubstrate.

In one embodiment stage 810 can be moved under long thin beam 808 usinga stepper or translator. In this way the portion of panel 809 that isunder beam 808 can be controlled so that various parts of panel 809 canbe processed. In one embodiment, panel 809 can be an amorphous siliconcoated glass panel. Thus, beam 808 can be used to melt a silicon filmsurface on panel 809.

An optical system was developed to create the optimal beam shape. In oneembodiment the optimal beam shape can be long enough to cover the entirewidth of a substrate and narrow enough to optimize the crystallizationprocess. Particular care can be taken with the design of the projectionoptics contained in the optical system to ensure thermal stability andcontrolled Depth of Focus (DOF) under high power loads, and to maximizethe optics lifetime.

In one embodiment, to ensure rapid motion in the scan direction, thelaser must operate at a high repetition rate, for example, at 6 kHz, andthe stage speed can, e.g., be 12 mm/sec for an approximately 2 micronpitch. The substrate can be exposed in a single pass, which requiresapproximately a 200 mJ/pulse to expose a Gen4 substrate. In oneembodiment a thin beam crystallization system with a 6 kHz, 900 W lasercan process an entire Gen4 panel in as little as 75 seconds.

A more detailed explanation of example embodiments of a surfacetreatment system 800 that can be used in accordance with the systems andmethods described herein are described in U.S. application Ser. Nos.10/781,251; 10/884,101; 10/884,547; and 11/201,877.

FIG. 9 is a diagram illustrating an amorphous silicon coated glass panel900. Panel 900 can be processed using the systems and methods describedherein, to form circuit areas 904 and display areas 906, which can beused to form a plurality of single displays, such as display 916. Eachdisplay region 918 can be separated by an untreated, amorphous siliconregion 912. The circuit and display areas, 904 and 906 respectively, canbe formed by passing a laser beam 902 over panel 900 in the direction ofarrow 914. After panel 900 is processed to form circuit areas 904 anddisplay areas 906 different types of circuits, e.g., transistors, pixeladdressing transistors, i.e., TFTs, digital circuits, etc. can be formedon the silicon substrate.

The placement of circuit area 904 and display area 906 can, for example,be based on a predetermined layout or mapping of panel 900. This layoutor mapping can be pre-loaded or continuously fed to a controller suchthat step distances between laser pulses can be varied on a shot by shotbasis. One or more panels 900 can then be processed using thepredetermined layout of panel 900. For example, the panel can beprocessed using the TDX process described above.

Circuit area 904 and display area 906 can be used for differentpurposes, e.g., forming digital circuits in circuit area 908 and formingpixel addressing transistors in display area 910. Digital circuits andpixel addressing transistors can each have different requirements. Forexample, the display area can require a high degree of uniformity forthe pixel addressing TFTs, otherwise visual artifacts, generallyreferred to as “mura” can result in the display. This can be especiallytrue for displays using OLEDs.

Implementations of laser based annealing methods such as ELA, SLS andTDX can result in mura. The source of mura can vary depending on thetechnique used to make the display area 910. For example, for an ELAprocess the mura observed can be called shot mura. Shot mura can formwhen the laser energy varies from shot to shot, and particularly whenthe step size is approximately the same size as the transistor channelthat will ultimately be deposited on the silicon film. ELA can use a 400μm wide beam with a step size of 10-20 μm. The transistor channeldimensions are generally also on the order of 10-20 μm. Variations inthe energy from one laser shot to next can cause variation in thematerial uniformity.

Digital circuit area 908 is generally not going to be seen andtherefore, visual artifacts such as shot mura are generally notimportant. Performance can, however, be important in digital circuitarea 908 because, for example, high performance can lead to higher speeddigital circuits.

As a result of the different requirements, it can be desirable to usedifferent processing techniques on different areas of panel 900. Forexample, a process that produces greater uniformity can be used indisplay area 906, while a process that produces higher quality can beused in circuit areas 904. In one embodiment, for example, a moretraditional ELA type process can be used for display areas 906, whilethe TDX process described above is used in circuit area 904. Further, byusing the same tool, e.g., system 800, as used for the TDX processdescribed above, a much smaller beam width can be used for the ELAprocess, e.g., 20 μm vs. 400 μm. A smaller step size, e.g., 1 μm, canalso be used, resulting in more shots per area as compared to thatachieved with conventional ELA tools. This will provide more averagingacross each transistor in display area 906 and the reduction of the ELAshot mura that conventional tools produce. Further, since the same toolcan also perform the TDX process, high performance circuit areas 904 canbe produced on the same substrate in one pass of beam 902.

Accordingly tool 800 can be configured to perform ELA in a low energymode, where the Si film is not completely melted during exposure, incontrast to the normal mode described above where each pulse fully meltsthe Si film. If the optimal energy density and step size combination arechosen, the resulting material can be small-grained uniformpoly-silicon. It should also be noted that it can be preferable totailor the average grain size to be many times smaller than thetransistor channel dimensions to fit a large number of grains within theactive device area and induce a large amount of averaging.

Thus, the energy density of incident beam 902 on substrate 900 can beswitched to the energy normally used in TDX processing when the beamfalls on regions where it is desirable to have high-qualitydirectionally-solidified poly-Si, e.g., in regions 904, and reduced to alevel below the energy needed for complete melting of the film whenscanning regions used for pixel addressing, e.g., regions 906. In thismanner, displays 916 can be produced by combining different modes ofoperation, i.e., a low energy mode and a high energy mode.

While certain embodiments of the inventions have been described above,it will be understood that the embodiments described are by way ofexample only. Accordingly, the inventions should not be limited based onthe described embodiments. Rather, the scope of the inventions describedherein should only be limited in light of the claims that follow whentaken in conjunction with the above description and accompanyingdrawings.

1. A device for processing a substrate comprising: a laser configured toproduce laser light, the laser configured to have a high energy mode anda low energy mode, the high energy mode configured to produce lightenergy sufficient to completely melt a silicon film, and the low energymode configured to produce light energy that is not sufficient tocompletely melt a silicon film; beam shaping optics coupled to the laserand configured to convert the laser light emitted from the laser into along thin beam with a short axis and a long axis; a stage configured tosupport the substrate and film; and a translator coupled with the stage,the translator configured to advance the substrate and film so as toproduce a step size in conjunction with the firing of the laser, whereinthe translator and the firing of the laser are configured to produce asmaller step size in the low energy mode when compared to the step sizeof the high energy mode.
 2. The device of claim 1, wherein the lowenergy mode is used to process a display area.
 3. The device of claim 1,wherein the high energy mode is used to process a circuit area.
 4. Thedevice of claim 1, wherein the beam width in the short axis when the lowenergy mode is used is approximately 20 μm.
 5. The device of claim 1,wherein the step size when the low energy mode is used is approximately1 μm.
 6. The device of claim 1, wherein the step size when in the lowenergy mode is configured such that approximately 10 shots of the laseroccur across the width of an electronic device that can be formed on thesubstrate.
 7. The device of claim 1, wherein the step size in highenergy mode is configured to be near a theoretical maximum step size. 8.The device of claim 1, wherein the high energy mode producesapproximately 750 mJ/cm² at the surface of the substrate.
 9. The deviceof claim 1, wherein the low energy mode produces approximately 250mJ/cm² at the surface of the substrate.
 10. The device of claim 1,wherein the step size when the high energy mode is used is approximately5 μm.
 11. The device of claim 1, wherein the step size when the highenergy mode is used is approximately 2.0 μm.
 12. The device of claim 1,wherein the device is configured to process a glass panel coated withamorphous silicon.